The overall goal of this proposal is to understand how kinetochores attach to spindle microtubules arid how this attachment is maintained and used to generate force for chromosome movements during mitosis. How chromosomes faithfully segregate during mitosis is an essential issue, as errors in this process can lead to aneuploidy, which in turn, leads to cell death, cancer, and birth defects. This proposal focuses on the protein Nuf2, which is a likely candidate for involvement in microtubule attachment and chromosome movement, but one that has not yet been investigated for a role in mitosis in vertebrate cells. The major goals of this project are to determine the assembly dynamics and function of Nuf2 at the vertebrate kinetochore and to identify any functional complexes containing Nuf2 that may operate in mitosis. To achieve these goals, the proposal has the following aims: (1) To determine if Nuf2 is at the kinetochore-microtubule interface in vertebrate cells and to test the stability and turnover rate of Nuf2 at vertebrate kinetochores, (2) To test the effects on function and structure of kinetochores in cells lacking functional Nuf2, and (3) To determine the microtubule binding properties of Nuf2 and to identify any Nuf2-binding proteins / Nuf-2 containing complexes.